1. Field of the Invention
The invention generally relates to the techniques for handling random access procedures, and more particularly, to apparatuses, systems, and methods for handling random access procedures in a multi-carrier system.
2. Description of the Related Art
In order to meet user demands for higher data rates in wireless communications, support for wider transmission bandwidths is required. A so-called Carrier Aggregation (CA) technique has been proposed to allow for the expansion of effective bandwidth delivered to a user terminal through concurrent utilization of radio resources across multiple carriers. The CA technique is most useful when it is difficult to derive a contiguous and extra wide bandwidth. With the CA technique, 2 or more frequency bands may be aggregated to form a larger transmission/receive bandwidth. Each of the aggregated frequency bands is generally referred to as a carrier frequency.
Specifically, each carrier frequency needs to be configured and activated before it may be used for data transmission or reception. The network side may first transmit a Radio Resource Control (RRC) message to configure the carrier frequencies for a User Equipment (UE) (or may be referred to as a Mobile Station (MS)), and then transmit a Medium Access Control (MAC) activation command to the UE to activate one of the carrier frequencies. After that, the UE may initiate a random access procedure on the activated carrier frequency for uplink timing alignment, requesting radio resources, or other purposes. However, if a UE is configured with more than one carrier frequency, there may be a situation where multiple random access procedures are requested to be performed on different carrier frequencies at the same time for the UE. However, in some radio access technologies, such as the Long Term Evolution (LTE) technology, only one random access procedure is allowed to be performed at a given time for a UE. As a result, confusion regarding which one of the random access procedures should be performed first may occur, which causes indeterminate behavior or even malfunction of the UE.